teams <- c(rep("yankees", 40), rep("padres", 40), rep("mariners", 40), rep("dodgers", 40))
salary <- c(rnorm(40, mean = 25), rnorm(40, 16), rnorm(40, 23), rnorm(40, 15))
df <- data.frame(teams, salary)
head(df)
## teams salary ## 1 yankees 25.33182 ## 2 yankees 26.94447 ## 3 yankees 23.31511 ## 4 yankees 24.59621 ## 5 yankees 27.25990 ## 6 yankees 25.57731
# population mean mean(~salary, data = df)
## [1] 19.74168
# SRS mean(~salary, data = sample(df, 40))
## [1] 20.34939
# Stratified sample
strat.samp <- rbind(sample(subset(df, teams == "yankees"), 10), sample(subset(df,
teams == "padres"), 10), sample(subset(df, teams == "mariners"), 10), sample(subset(df,
teams == "dodgers"), 10))
mean(~salary, data = strat.samp)
## [1] 20.00718
Control: Compare treatment of interest to a control group.
Randomization: Randomly assign subjects to treatments.
Replication: Within a study, replicate by collecting a sufficiently large sample. Or replicate the entire study.
Blocking: If there are variables that are known or suspected to affect the response variable, first group subjects into blocks based on these variables, and then randomize cases within each block to treatment groups.
A study is designed to test the effect of light level and noise level on exam performance of students. The researcher also believes that light and noise levels might have different effects on males and females, so wants to make sure both genders are represented equally under different conditions. Which of the below is correct?
Placebo: fake treatment, often used as the control group for medical studies
Placebo effect: experimental units showing improvement simply because they believe they are receiving a special treatment
Blinding: when experimental units do not know whether they are in the control or treatment group
Double-blind: when both the experimental units and the researchers do not know who is in the control and who is in the treatment group
How do you test if acupuncture reduces pain?
"Sham acupuncture" is a good control.